Compressor control system



y 1961 c. A. CORSON ET AL 2,982,467

COMPRESSOR CONTROL SYSTEM 3 Sheets-Sheet 2 Filed March 6, 1956 ST2(OLOSED POSITION IN E TRZBO EXAUST GTED m F/G. 2 MOTOR POWER LINE TRICO OFW CON ELECTRIC MOTOR N n 03 TR N06 E05 V W VALVE THEIR ATTORNEY B. H. P.

C.F.M.@ INLET May 2, 1961 Filed March 6, 1956 IOO 200 5 Sheets-Sheet 3 FIG. 5 I

DISCH. P.S.I.A.

' e60 960 INVENTORS CHARLES A. CORSON WADE W PASCHKE THEIR ATTORNEY Un t d S es Pat fl io COMPRESSOR CONTROL SYSTEM Charles A. Corson, Painted Post, N.Y., and WadeW.

Paschke, Mountain Lakes, N.J., assignors to Ingersoll- Rand Company, New York, N .Y., a corporation of New Jersey Filed Mar. 6, 1956, Ser. No. 569,782

12 Claims. (Cl. 230-25) This invention relates to control systems and more particularly to load controllers for motor driven gas compressors.

The control of this invention is designed particularly for use in compressor installations wherein the motor load varies throughout a loading cycle because of variations in inlet or discharge pressure of the compresor, and more particularly to such installations wherein the overall variations in such pressure is in one d rection onlyi.e., an overall pressure increase or pressure decrease. An example of such an installation is where a compressor is connected to fill a container with a gas, compressing the gas from a pressure of, for example, 100 pounds per square inch (p.s.i.) to 900 p.s.i. Without a load control, or regulator, the compressor driving motor would have to be, in such an installation, of sufiicient horse power to compress the gas from 100 p.s.i. to 900 p.s.i. at the full capacity of the compressor. However, the maximum horse power demand on the motor would occur during only a relatively short period of time at the end of the cycle.

With the present invention, the compressor capacity is controlled in response to the load on the motor in such a manner that the compressor is unloaded in a step by step fashion so that as the discharge pressure of the compressor increases; the capacity of the compressor is proportionately reduced. Moreover, this control is designed to unload the compressor in such a fashion that the driving motor is operated at approximately its rated horse power during the entire cycle. Inasmuch as the control is operated in accordance with the load on the driving motor, the controller will operate effectively regardless of the value of the inlet pressure within broad limits-so long as this value remains relatively constant throughout a load cycle once the cycle has started.

It is one object of this invention to provide a control for motor driven compressors adapted to operate in installations wherein the inlet or discharge pressureof the compressor varies over a wide range during a cycle, whereby the compressor capacity is controlled to load the driving motor to substantially its full rated capacity over the entire cycle.

A further object is to provide such a control with a safety control operating substantially independently of the control actuated in response to variations in motor load.

Further objects will become apparent from the following specification and drawing in which,

Fig. l is a diagrammatic view of the unloader,

Fig. 2 is a schematic view of the details of a portion of the unloader,

Fig. 3 is a schematic view ,of a compressor to be controlled,

Fig. 4 is a graph showing the brake horse power of the motor compared to the discharge pressure of the compressor, and

Fig. 5 is a graph showing the quantity of air pumped by the compressor for a given discharge pressure.

2,982,467 li d. M x 2. 9. 1.

, 2 OPERATION AND CONSTRUCTIQNIN GENERAL Loading the compressor a f Referring to the drawings, and first to Fig. 3, th compressor controlled by the unloader is illustrated as a two stage compressor driven by an electric motor 8 and having three low pressure stage compressors 10,

' 12 and 14 and three high pressure stage compressors 16,

18 and 20. All of the compressors are provided with solenoid operated free air unloader valves, designated by PAUL FAU3,. FAUS and FAU8, there being one such valve at 'each'end of each compressor, and there is provided additionally'clearance pocket valves, designated by CP2 and CP4, for two of the low pressure compressors .12 and 14. Thus positioned eachsuch clearanceor unloader valve controls part only of'the compressor capacity. Each valve is connected with a means, or valve operating mechanism, for being separately operated, which means can be of any conventional form such as the air operated diaphragm 22 connected for the supply of actuating fluid through a three way solenoid operated valve 26 (identified in general by UNLZin Fig.2). I I

In installations wherein the starting discharge pressure of a loading cycle is relatively low and the final pressure is relatively high, it is normally desirable to load the compressor to one-half or two-thirds of its ca' pacity in one step and thereafter complete the loading of the compressor in a plurality of small loadingsteps. The degree to which the compressor is loaded in the first step is determined by the particular installation. It is generally known what the normal range of initial and maximum discharge pressures will be for any given installation, and accordingly, the control is designed to initially load the compressor to a capacity, for a given discharge pressure, which will closely approximate'a load on the driving motor at or near the rated capacity of such motor. I

With the control disclosed it is assumed byway of example that it is desirable to initially load the compressor to approximately two-thirds of its capacity. Ac cordingly, the UNLS valve operating mechanism operates to close all FAU8 valves thereby substantially fully loading the high pressure stage of the compressor and loading the low pressure stage to one-half capacity. Thereafter the low pressure stage .is loaded to "full" capacity in a step by step fashion by the means for operating other valves'e.g, UNLl, UNL3, closing, in

sequence, the valves FAUl, FAU3, FAUS and CP2 and quence timer ST is energized to close. in numerical 'order I the switches ST1, ST2, ST3, etc. The timer ST-may be of any commercial form adapted to close the switches ,in delayed sequence. .For. example it may be desired to close one switch every ten seconds after the. cornpressor is started such that the low pressure stagesare completely loaded in 50 seconds.

Load responsive unloading of compressor Additionally connected to and cooperating with the loading control is the unloading control designed. to prevent the load on the motor from exceeding the rated horse power. This unloading control includes a control element, such as a. contact making watt meter (CFW) and'associated switch elements, responsive to 3,1 variations in load on the driving motor and connected to the means for operating, the unloading valves.

The control element isenergized and de-energized alternately as. the motor-load exceeds, and falls below a predetermined value. Each, time the control element is energized it operates said means to partially unload the compressor and reduce the motor load. More. particularly, whenever the load on the driving' motor exceeds, for example, 1,050 horse power, the watt meter is closed, or energized, thereby operating, through appropriate connecting elements, the means for opening one of the unloading valves. The operation of the unloading valve lowers the capacity of the compressor approximately one-twelfth which lowers the horse power demand on the motor to say, for example, 950 horse power. This lowering of the power demand below the 1,050 value de-energizes the watt meter. Thereafter theload on the compressor will increase proportionately with the increase in discharge pressure of the compressor until such time asthe load on the motor again exceeds 1,050 thereby energizing the watt meter to again further unload, or reduce the capacity of, the compressor.

Time delay unloading of compressor In the event the discharge pressure condition or-loading condition at anytime in the cycle is such that when the watt meter is energized to partially unload the compressor and the unloading step is not sufiicient to reduce the motor load to a valuewhereat the watt meter is de-energized, a safety time, delay control comes into operation to reduce the capacity of the compressor. This safety control is energized to operate the next unloading step of the cycle in the event the watt meter is not tie-energized within a predetermined lapse time (e.g., 3 seconds) after being energized. If this additional unloading step is not sufiiciently great to drop the motor load below value at which the watt meter is de-energized, then 4 seconds later the safety mechanism will trigger the succeeding unloading step and. so on until the motor load is dropped to a value whereat the watt meter is de-energized.

It is to be noted that the safety timedelay is set such that under normal operating conditions the watt meter is derenergized before the safety device. is operated to further unload the compressor. Inasmuch aswatt meter and safety device are de-energized at: the same time, it is immaterial to the operation ofthe control how long it takes before the load-on the compressor builds up to a value whereas the watt meter is again energized.

CONSTRUCTION IN DETAIL. Loader Referring now in more detail to the particular construction of the control shown by way of illustration,

Fig. l is a diagrammatic view'ofthe variouselements involved and show their interconnections. These elements are of the electrically operated type and are shown connected between power lines 28 and 30. The solenoid unloading valve UNL8 comprises a three Way valve eement similar to valve 26 (Fig. 2) connected to a purality of motors similar to motor 22, one motor being provided for each FAU8ivalve. When the compressor is started, UNL8 is energized to operate all F'All8 valv s to load the compressor to approximately /5 of its capacity.

Energized simultaneously with UNL8 is UNL7 to close FAU7. Connected in series with UNL7 is a normally closed pressure switch PS connected to the discharge of the compressor and des'gned to open when ever the discharge pressure exceeds some predetermined value, as for example, 800 p.s.i. Opening of PS deenergizes UNL7 to open FAU7. The circuit containing UNL7 is provided merely to insure that too great a pressure differential can not exist across the high pressure stage. Thisis, a. desirable safety. feature, but his .4 not a feature necessary to the operation of the unloader.

Connected to the remaining valves are time delay elements ST and ST1-ST5 for completing the loading cycle specifically. Sequence timer ST is also energized simultaneously with UNL7 and UNL8 and is connected to operate in time delayed sequence the switches STI- STS. These switches STl-STS and solenoid unloader valves UNL1-UNL5 are connected, respectively, in circuits 32, 34, 36, 38 and 40 so that as each switch is closed, the numerically corresponding unloader valve is energized. It will be assumed for purposes of illustration that the sequence timer is designed to close the switches STl-STS in numerical order at 10 second intervals after the compressor is started and that UNLI is connected to operate FAUl, UNL2 is connected to opcrate CP2, UNL3 is connected to operate FAU3, UNL4 is connected to operate CP4, and UNLS is connected to operate FAUS.

With the loading circuit described, upon supplying power to lines 28 and 30, UNL7 and UNL8 are immediately energized to load the compressor to approximately two-thirds of its capacity. Ten seconds later the sequence timer closes STI thereby completing circuit 32 to operate UNLl closing free air unloader valve FAUl to further increase the capacity of the compressor; ten seconds after the operation of STI, the sequence timer closes ST2 to complete circuit 34 and. operate UNL2 closing clearance pocket CP2 to further increase the compressor capacity. Then 8T3, ST4 and ST5 are closed sequentially at ten second intervals to close FAU3, CP4 and. FAUS, respectively, to completely load the compressor.

Unloader Interconnected with the loading circuit is the unloading circuit which cooperates with but operates substantially independently of the loading circuit to maintain the load on the driving motor at or slightly below its rated capacity by controlling the capacity of the compressor. More particularly; this circuit includes the contact making watt meter CFW in circuit 42 in which circuit a master relay RA is connected to be energized and deenerg'zed by the closing and opening of CFW. The relay RA is, in turn, connected to operate the master elements or switches RA! and RA2 connected in con trol circuit 44 and set up circuit 46, respectively. Each master switch RAl. and RA2 is connected through branch circuits to control a plurality of control elements or relays Rl-Rll, with RAI connected to control the odd numbered control relays (e.g., R1, R3) and relay RA2 being connected to control'even numbered auxiliary relays (e.g., R2, R4). The control relays are connected to operate a plurality of switches identified by RM, Rlb, R2a, R2'b, and so on, with all switches with an R1 prefix being controlled by the R1 control relay, all prefix R2 switches being controlled by the R2 relay and so on.

It is to be noted that all R prefix switches are'shown as being either normally open or normally closed (the switches shown closed across the schematic points are normally closed). Whenever the relay controlling the particular switch is energized, the switch action, is reversed. For example, RAl, is anormally open switch and accordingly when the relay RA is energized, RAI is closed, whereas switch RA2 which is normally closed is simultaneously opened. When the relay RA is deenergized, the normally'open switch RAl will open and the normally closed switch RA2 will close.

The RAI circuit 44 comprises a plurality of branch circuits 44a, 44b, 44c, 44d, Me and 44), connected in parallel relative to each other but in series with the switch RAl. Connected in branch circuit 44a is a normally closed'switch R2c and in branch 44) is a normally open switch RlOb. Connected in each of the other branch circuits 44b, 44c, 44d and 44a is a normallyopenswitch and a normally closed switch identified, respectively, as R212 ancLRlC, R411ancLR6c, R6b.and.R8c,,and.R8b and 1410c. Connected respectively, in branches, 44a, 44b, 44c, 44d, 44c and 44) are control relays R1,'R3, R5, R7, R9 and R11 each of which is in turn connected to operate a switch in the loading circuit having the same letter and numeral prefix. These switches are designated Rlc, R3d, R511, Re, R7d, RM and Rllb, and are connected, respectively, in the loading circuits 32, 34, 36, 34a, 34a, 38 and 40.

With this arrangement when R1 of the unloading system is energized, switch Rlc will be opened to break circuit 32 and thereby operate UNLl. Similarly, when R3 of the unloader circuit is energized, switch R3d is opened to operate UNL2 and so on. In other words, whenever one of the branch circuits of circuit 44 is completed, the compressor is partially unloaded.

The unloading circuit 46 is similar to circuit 44 and comprises a plurality of branch circuits 46a, 46b, 46c, 46d and 462 connected in parallel relative to each other but in series with the switch RA2. Connected in each branch circuit 46a-46e, respectively, is a normally open switch and a normally closed switch identified, respectively, as Rlb and R3c; R3b and R5e; RSb and R70; R7b and R90; and R9b and R110. Also connected respectively, in branches 46a-46e are control relays R2, R4, R6, R8 and R10 each of which in turn is connected to operate the switches in the control circuit having the same and Rlla is connected between 462 and 44 With the circuits 44, 46 and 32-40 just described everytime the CFW is closed, after the first step, a branch circuit of 44 is closed to (a) Open a switch (R3c) in the preceding branch circuit (46a) of circuit 46 to prevent premature operation of the succeeding 46 branch circuit (46b),

(b) Closes a switch (R3b) in the succeeding branch circuit of circuit 46 (46b) to set up this circuit to be completed on subsequent closing of RA2,

(c) Closes a preceding cross switch (R3a) to lock in the energized circuit, by locked in energized it is meant that subsequent opening of the switch RA1 will not deenergize that branch circuit, and

(d) Breaks one of loading circuits (opens R3d) to partially unload the compressor. (All numerals within parentheses in (a)-(d) are by way of illustration.)

Whenever the CFW is opened, a branch circuit of circuit 46 is completed to carry out steps (a) and (b) and (0) just described, except relative to preceding and succeeding branch circuits of circuit 44.

OPERATION CIRCUITS 44 AND 46 The operation of each step of the branch circuits of 44 and 46 is substantially identical other thanthe first step of circuit 44. Accordingly, the operation of only circuits 44a, 44b and 46a of the load responsive unloading cir- (1) Opens switch Rlc in circuit 32 thereby 'de-e n elrgizing UNLl such that FAUl is opened to partially unload the compressor and (2) Closed switch Rlb in branch circuit 46a setting up this circuit to be triggered by the subsequent closing of switch RA2. J (3) Closes switch Rla locking Rlin circuit 48 such that subsequent operation of the switch RA1 willinino The partially unloading of the-compressor will result in the lowering of the horsepower demand on the motor such that it falls below 1,050 brake horse power and the Watt meter CFW will open thereby de-energizing RA to open RA1 and close RA2. Closing of RA2 completes branch circuit 46a energizing R2 which simultaneously;

(1) Open switch R20 to prevent premature triggering of unenergized branches of circuit 44, and r (2) Closes 'R2b setting up circuit 44b to be triggered by the subsequent closing of RA1, and i (3) Locks in with circuit 48 by closing switch R24.

Thereafter if the horsepower demand on the motor again rises above 1,050 brake horse power, the contact making watt meter at CFW will close energizing RA to close RA1 and open RA2, completing branch circuit 44b, energizing R3 to (1) close R3a locking in R3 through line 48, (2) close-R3b to set up circuit 46b, (3) operate R3d to de-energize UNL2 and open clearance pocket CP2 and further unload the compressor, and (4) open R30 to prevent premature triggering of unenergized branch circuits of circuit 46.

Alternate opening and closing of the CFW in response to the load demand on the motor will thereafter energize circuit 46b to set up 440, then trigger circuit 44c to operate UNL3 (and energize UNL2 by closing R5e to close CP2 if branch circuit 34a, described hereinafter, is used), then to complete circuit 460 to set up circuit 44d to be subsequently triggered to again operate UNL2 and open CP2 where circuit 34a is used, then complete circuit 46d to set up circuit Me to be triggered to operate UNL4, then complete circuit 46e to set up circuit 44 to be triggered to operate UNL5 and thereby complete the unloading cycle.

It is to be noted that a parallel circuit 34a is provided in line 34 connected on the opposite sides of switch R3d. This parallel circuit includes a normally open switch R5e and normally closed switch R7d. The purpose of this parallel circuit is to give a finer degree of load control without increasing the number of clearance pockets or loading valves. More particularly it'operates to c1os'e clearance pocket CP2 at the same time FAU3 is opened; and to open it subsequently when R7d operates. This' circuit may or may not be used as desired without otherwise efiecting the operation of the control system.

TIME RESPONSIVE UNLOADER Q Structure Cooperating with the loading and unloading systems or circuits is the time delay mechanism energized and dpenergized simultaneously with the CFW and interconnected with the circuits 44 and 46. This mechanism acts within a predetermined time after the CFW is closed to complete one of the branch circuits 46 and ing stages of the cycle.

ing steps of the cycle and this unloading step 'i'sQnot sufiicient to drop the load on the motor to something below 1,050 brake horse power to open the CFW, then the time delay mechanism comes into operation to further unload the compressor in a step by step fashion until such time as the horse power load on the motor drops below 1,050 thereby opening the CFW.

The time delay mechanism comprises the following time delay circuit. A pair of time delay switches TRlro and I R210, connected in a series in circuit 42 on the opposite sides of the CFW, and switch TRltc connected in circuit 48. The TR1 switches are controlled by a timing relay TR1 connected in circuit 42 and in parallel with switch TRlto. The TRZto switch is controlled by a timing relay TR2 connected in series in circuit 48.

It is to be noted that the switches designated of the suflix to are of the type which when the associated timing relay is energized will open within a predetermined time thereafter if the timing relay remains energized, and will close immediately when the timing relay is de-energized. The switch TRltc is of the type that closes within a predetermined time after the timing relay TR1 is energized, but opens immediately when the timing relay is de-energized. The time delay of these switches are set such that, for any given installation, the unloading circuit controlled by the watt meter CFW will normally control the unloading of the compressor-i.e., the delay in operation of these switches is sufiiciently long to permit the unloading circuit to operate and complete one unloading step of the cycle before the time delay mechanism comes into operation. Thus the time delay mechanism serves only as a safety device where any one unloading step is not sufficient to lower the horse power demand on the motor to something less than the value at which the watt meter is opened.

Operation The operation, in detail, of the time delay mechanism is as follows. Whenever the watt meter CFW closes completing circuit 42, the timing relay TR1 is energized so that TRlto and TRltc open and close, respectively, in for example three seconds. Assume during this three second period that the unloading circuit controlled by the CFW has triggered circuit 441: and partially unloaded the compressor by operating UNLI, and that this unloading step is not sufficient to lower the horse power load on the motor to a value low enough to open CFW. Then, on the expiration of three seconds, TRltc closes completing circuit 48 thereby energizng the timing relay TR2 which, in turn, energizes TR2t0 such that it will open in approximately one second.

' energized.

After a lapse of one second from this operation, TR2to opens thereby de-energizing TR1 and immediately closing switch TRlto and opening TRltc to de-energize TR2 and thereby close TRZto completing circuit 42. This action is the same as if CFW closed, hence RA is en- .ergized to close RAl completing circuit 44b to operate UNL2. This completes One step of the timing cycle and one complete step of unloading of the compressor.

This timing unloading step is continuously repeated, taking a total of four seconds for each step, with one of the solenoid unloading valves UNL being operated by every completed step of operation of the time delay mechanism.

The time delay mechanism will continue to operate to unload the compressor in a step by step fashion and in the same manner as if the CFW were opening and closing until such time as the load on the compressor falls below a value at which the CFW is opened thereby deenergizing TR1 and halting the operation of the time delay mechanism. 1 The foregoing operational steps are shown diagrammatically hereinafter, but it is to be understood that the.

diagram portion relating to the time delay circuit occurs only if the CFW is not opened within three seconds after it is closed.

DESCRIPTION OF FIGURE 2 Referring now to Figure 2, the auxiliary relay RA and control relays R1-'R5 are shown in detail. Onlythe details of this portion of the circuit is shown, for, as previously mentioned, the remaining portion of the circuit will become obvious and is substantially a repetition of what is shown. It is apparent that by merely adding additional branch circuits to 46 and 44, the number of unloading steps may be multiplied indefinitely without changing the general pattern of control.

It is assumed that R1 and R2 have been previously energized and locked in position so that switches Rla, R112, R2a, and R2b will remain closed and Rlc and R2c will remain open for the remainder of the loading cycle. Moreover it is assumed that the CFW has just closed thereby energizing RA to close RAl and open RA2. The closing of RA]. energizes R3-(circuit 44b is completed through switch R2b, R40, and thence through the control relay R3). As shown R3 has just been energized there by closing switches R311 and R3b and opening switches R3c and R311.

Opening of switch R311 de-energizes the three-way solenoid of UNL2 to exhaust air from the valve unloader 22 and hence operates clearance pocket CP2 to partially unload the compressor. The opening of R31: prevents the completion of the branch circuit 46b through Rlb, R211 and thence back through R112 to line 48.

The closing of R3a completes a circuit through R212 and Rla to lock in relay R3. The closing of R312 sets -up branch circuit 46b such that on subsequent opening of CFW to close RA2 it will complete circuit 46b.

When RA2 closes, it completes a circuit 46b through R315, R5c and actuates R4 into its alternate position closing switches R411 and R4b and opening R4c. Closing of R411 locks in control relay R4 through R311, RM and R112. Closing of R412 sets up circuit 440 to be triggered by subsequent closing of the CFW, and opening of R40 prevents premature triggering of circuit 441: through R212, branch circuit 44b, R3a, R212, Rla, and line 48.

DESCRIPTION OF COMPLETE LOAD CYCLE Reviewing briefly a full operating cycle of the motor compressor unit, the steps are as follows:

Step A.Assuming the compressor is started unloaded, the control circuit is energized thereby energizing UNL8 and closing the eight FAUS valves to load the compressor to approximately two-thirds of its capacity.

Simultaneously, with this action UNL7 is energized, assuming the discharge pressure of the compressor is below a value at which switch PS will be opened, and accordingly FAU7 is closed.

Step B.--Energized simultaneously with the energizing of the control circuit is the sequence timer ST which operates the switches STl-STS in numerical order at, for example 3'0 second intervals thereby operating in sequence and at the same interval UNLl-UNLS to close FAUl, CP2, FAU3, CP4 and FAUS and fully load the compressor in a step by step fashion.

Step C.Assuming the discharge pressure of the compressor reaches a value whereat the motor load exceeds some predetermined value corresponding approximately to the rated horse power of the compressor (e.g. 1,050

, horse power), the contact making watt meter CFW will close energizing RA to complete and lock in circuit 44a and thereby operate R1 to open circuit 32 and 'deenergize UNLl and open FAUl to partially unload the compressor.

Step C reverse.-Assuming the operation of FAUl lowers the demand on the motor to a value below 1,050 horse power, the CFW will open triggering and locking in branch circuit 461: to set up branch circuit 44b.

Step D.-When the motor load again exceeds 1,050 horse power, CFW closes energizing RA to complete and lock in circuit 34, de-energizing UNL2 and opening CP2.

Step D reverse.When the load demand falls below 1,050 horse power, the CFW opens, circuit 46b is com pleted to set up circuit 44c.

Step Ed-When CFW again noses, circuit 4 1C" is triggered completing circuit 34 through the by-pass circuit predetermined value, circuit 46d is completed to set up circuit 44e.

Step G.Whcn the CFW closes, circuit 44a is triggel-ed to break circuit 38 and open (2P4.

Step G reverse.When the CFW again Opens, circuit 462 is completed to setup branch circuit 44f.

Step H.On closing of CFW, circuit 44) is triggered to break circuit 40 and open FAUS.

If at any time during the unloading cycle, steps -0, the Operation of one of the unloading steps is insufficient 'to' lower the horse power demand on the driving motor to a value whereat the watt meter will open, then within some predetermined time from the initial closing of the CFW, the time delay circuit'mechanism comes into operation to unload the compressor in steps having approximately a four second interval therebetween. The unloading sequence by the time delay mechanism is identical to that specified for the CFW, the only difference being that there is a four second interval between each complete step (eg. it requires 4 seconds to complete step D, Step D reverse) in the case of the time delay mechanism, whereas with the CFW, the time between steps will vary depending on the load variationson the motor.

(STEP A) UNLB loads compressor partially (STEP 13) ST load com- DI'PSSOI' 1.0 full capacity (STEP 0) CFW Closes enerrizing TRI RX O ens I Closes TR1-t.c. TR1-t.o. RA2 RAI Closes in 3 Opens in 3 sec. sec. de- Energize energize RA R1 starting l step C-reverse Closes Open eir ifirzgize Rla Ric (Loclrs in B1) Rib TR2-t.o. de-energlze o ens in 1 sec. UNLl opens p .FAUl

de-energize TRl lowers .p. to

less than 1050 orenlmz CFW to start "step 0 Close Owens reverse TRl-Lo. IRl-t.c.

tie-e ergize 'IRz Closes TR2-t.o. Completes RA Circuit starting Step D (STEP C reverse) 46c is V ageants p I .5 (STEP Creverse) CFW opens de-ene'glzlng Switches now "locked in" closed Ria-Rlb locked in" open, Ric

TRl RA (Resets time delay 7 circuit) Close Open HA2 'BAl energize O ens Closes R2c R2a (locks in R2) When h.p. exceeds 1050, CFW closes starting Step D (STEP D) CFW close Switches now locked in closed Rla-Rlb-Rza-Rzb energize locked in open. R20 1 R10 m RA 7 S e STEP 0 e Closes Opens RAl RA2 energize R3 Clo es i Opens R311 locks in R3) R3c R3b 33d deeuerglze UN L2 Opens CP 2 lowers h.p. to less than 1050 opening A CFW to start "Step D reverse" Step D reverse: Operates Resets time delay circuit. Locks in open lt-lc. Looks in closed R4a, R41).

tep E Starts time dela circuit. Dc-euergize UN 3 Energize UNL2 Locks in "open" Rag, Rad Locks in "closed" Baa, Rab, R56. Step E reverse:

Resets time delay circuit. Locks in open" R60. Locks in closed R611, R6b.

Starts time delay circuit. Dre-energize UNXA V Locks in "open" R9c. R9d.

Locks in "closed" R9a-R9b. Step G reverse:

Resets time delay circuit. Locks in pen" R100. Iigcks in c osed" RlOa, R100. P 1 Starts time delay circuit. De-energize UNLo Locks in "open" Rllb. R110. Locks in closed" R110.

While we have shown and described a specific form FAU3 Closes CP2 Step Opens (3P4;

Ste

Opens FAU5 otour invention, it is to ,be understood that various .cally responsive to variations in load on the driving motor connected to be energized and de-energized alternately and respectively as the motor load exceeds and falls below a predetermined value, means connecting said wattmeter to the first said means for operating the first said means to partially unload the compressor every time the wattmeter is energized, and a time delay mechanism energized and de-energized simultaneously with said wattmeter and connected so long as 'it is energized to operate the second said means after the lapse of a predetermined time from being energized for partially un-' loading the compressor.

2. The controller claimed in claim 1 in which said time delay mechanism while energized. repeatedly operates the second said means to unload the compressor in a step by step fashion with a lapse of a predetermined time between each step.

3. The controller claimed in claim 1 in which said time delay mechanism is operatively connected to said wattmeter and energized and de-energized thereby.

4. The combination with a motor driven compressor 'having a plurality of unloading valves, each valve controlling part only of the compressor capacity, of a load controller comprising a valve operating mechanism connected to some of said valves and operable on starting up the compressor to operate all ofthe valves connected thereto to load the compressor to the expected starting maximum load, means operatively connected for operating other of said valves, a control element automatically responsive to variations in load on the driving motor and energized and de-energized alternately as the motor load exceeds and falls below a predetermined value, means operatively connecting said control element to the first said means to partially unload the compressor every time the control element is energized, and a time delay mechanism energized and de-energized simultaneously 7:

5. The controller claimed in clalm 4 in which time dc lay elements are connected .to said. other of said valves operative on starting a loading cycle to closesaid-otller of said valves in delayed sequence. .to .load thecompressor in a step by step fashion.

6. The controller claimed in .claim 5 in which the delay between steps in loading is greater than the predetermined time lapse between operating steps of said time-delay mechanism.

7. The combination with-a motor driven compressor connected to pump gas under pressure discharged at a pressure varying over a relatively large range and having a plurality of unloading valves,.the overall ,variations being in one direction only, said compressor. including a low pressure stage and a high pressure stage with. each stage having valves with each valve controlling part only of the capacity of the stage in which-it is connected, of a load controller comprising valve operating mechanism connected to the high pressure stage valves andsome of the low pressure stage valves and operated'on starting up the compressor to operate all valves connected theretoto load the high pressure stage to substantially full-capacity Wariations in load on the driving motor. energized and deand to partially load the low pressurestage, means operatively connected for operating theremaininglow'pressure valves, a control element automatically responsive to .energizedaalternatelyas the motor load exeeeds-andfalls below a predetermined value,-means for operatively con- ;tnecting said controlelement to actuate said means .for partially unloading-the compressor every time the'con- -5 'trol element is energized, and a time delay mechanism energized and de-energized simultaneously with said con- ..trol element and connected so long as itis energized to :operate the last said means after the lapse of a predetermined time from being energized for unloading the com- 10 .pressor in a step by step fashion.

8. The'combination with a motor driven compressor havinga plurality .of unloadingvalves, eachvalve controlling part only of the compressor capacity, of a load .controllencomprising;. means operatively connected for 1 operating each of said valves; a contact making watt meter connected to the motor'power supply andenergized and de-energized alternately whenever the motor load ex'ceeds :and falls below a predeterminedvalue; a control electrical circuit comprising aplurality of parallel circuits each containinganormally .open switch, a normally closed switch anda control. relay, except the first actuated parallel cirtcuit does not contain the normallyclosed switch and the ;last actuated parallel circuit does not contain a normally closedswitch, anda master switch connected in series .with said parallel circuitsya setup electrical circuit comprising a plurality of parallel circuits each containing ;a

. normally open switch andnormally closed switch and an .auxiliary relay, and -a-master switch connected in series -with the last said parallel circuits and being operable. in 30. a reverse fashion to the first said master switch; interconenectingnormally open switches connecting the parallel circuits .of the control and setup circuits; and a master relay connected to be actuated by said contact making watt meter and connected to actuate said master switches;

" said auxiliary and control relays, except for the first and last control relay to be actuated, being connected to operate a switch in the succeeding and preceding, in operating order, parallel circuit and an interconnecting switch, and said control relays being connected additionally to operate said means such that whenever the contact making watt meter is actuated into one'position, one of the branch circuits of the control circuit is locked in energized to operate said means to partially unload the compressor and set up the succeeding branchcircuit of the set up circuit to be locked in energized by a reverse of operation of the contact making watt meter to set up the succeeding parallel circuit of the control circuit.

9. The load controller claimed in claim 8 in which is provided a time delay circuit including time delay opening ,50 and time delay closing switches and actuating relays thereforinterconnected with said contact making watt meter and control and setup circuits and arranged to be energized and de-energized with saidmeter and adapted in the event that the contact making watt meter is not de-ener- .55 gized within a predetermined length of time after being energized, to de-energize and energize the control and setup circuits in time delayed sequence in the same fashion as if the contact making watt meter were alternately de-energized and energized.

.60 10. The combination with a motor driven compressor connected to pump gas under pressure and discharge such gas at a pressure varying over a relatively large range and having a plurality of :unloading valves, the overall variations being in one direction only, said compressor includinga low pressure stage and a high pressure stage with each stage having unloader valves with each valve controlling part only of the capacity of the stage in which it is connected of a load controller; comprising a plurality of valve operating mechanisms connected to severally 370 operate said valves; a control element connected to the motor and operated in response to variations in load thereon to be actuated into alternate control positions by alternations of such load above and below a predetermined value; a control system having a master element and a plurality of actuatingelements connected to control the operation of said valve operating mechanisms; a setup system having a master element and a plurality of actuating elements controlled thereby; means connected to be operated by said control element and connected to each master element for actuating said master elements into different control positions each time the control element is actuated, said systems being interconnected such that each time the control element is actuated into one position, the master element of the control system is operated to power at least one of the associated actuated elements to actuate at least one of the valve operating mechanisms to partially unload the compressor, and each time the control element is actuated into another position the master element of the setup system is operated .to power one of the actuating elements controlled thereby to set up a part of the control system such that it may be activated when the control element is again actuated into the first said position.

11. The load controller claimed in claim 10 in which a time delay unloading system is interconnected with the control and setup systems and said control element is energized and de-energized whenever the motor load exceeds or falls below said predetermined value, and said time delay unloading system is arranged in the event the control element is not alternated into said other position within a predetermined lapse time from being actuated into the first said position to actuate said master control p I 5 elements in time delay sequence and in the same manner as if the control element was actuated into alternate control positions.

12. The load controller claimed in claim 9 in which References Cited in the file of this patent UNITED STATES PATENTS 1,528,547 Holveck Mar. 3, 1925 1,634,542 Holdsworth July 5, 1927 1,783,036 Crawford Nov. 25, 1930 1,912,463 Ploeger June 6, 1933 2,176,716 Jump Oct. 17, 1939 2,236,088 Doeg Mar. 25, 1941 2,253,159 Anderson et al Aug. 19, 1941 2,338,451 McCoy Jan. 4, 1944 2,602,582 Garbaccio July 8, 1952 2,646,919 Bartholomew July 28, 1953 2,730,296

Hartwell Jan. 10, 1956 

